This invention relates generally to truss structures, and more particularly, to strut and node assemblies for use in constructing high precision, reconfigurable trusses.
It is well known that large structures may be comprised of elongated struts and nodes that are coupled together to form trusses. Such structures are especially suitable when weight, height, stiffness, and strength are important factors, and increasingly, such structures are being utilized in conjunction with space and metrology systems requiring high precision and reconfigurability. To be suitable for such applications and possess the requisite stability (i.e. measured in the order of nanometers) to produce precision trusses with a high degree of structural integrity, it is necessary that the node/strut coupling assemblies be configured to substantially reduce non-linearity""s associated with hysteresis (i.e. the relatively slow deformation of the truss structure due to load and temperature stresses without a subsequent return to normal) and/or stiction (i.e., the sudden deformation of the truss structure, sometimes characterized by a xe2x80x9cpopxe2x80x9d or xe2x80x9csnapxe2x80x9d without a commensurate return to normal). Furthermore, such assemblies should be lightweight, relatively inexpensive, and simple and quick to assemble, since such trusses may comprise hundreds or even thousands of struts and coupling nodes. Finally, the strut/node assembly must of a nature that makes even an over constrained system reconfigurable so as to render the overall truss structure capable of being modified for different applications.
One known technique for interconnecting struts to form a truss utilizes clevis joints. That is, the joint comprises a unshaped piece of metal that has a space between the legs thereof. The portion of the member to be secured is positioned within the space, and a pin or bolt is passed through the legs and a portion of the member residing in the space. The bolt is then tightened to secure the member. Unfortunately, this mechanism forms a friction-joint that can slip causing possible variations in the length of the structure and/or angles between joined struts. Since variations are cumulative, the overall structure could suffer significant distortion. In addition to the above problem, such joints are heavy and there fore may not be suitable for space applications.
Another known technique for joining a strut to a node involves the use of internally threaded holes in a node and in a strut that is threadably engaged by a single externally threaded member (e.g. a bolt). First and second internally threaded nuts engage the externally threaded member in the region between the strut and the node and cooperate with the member to secure the strut to the node. The space between the strut and node may be adjusted by manipulating the nuts relative to the externally threaded member on which they are mounted. While this arrangement does not suffer the disadvantage that is associated with respect to the previously described known technique, the joints formed are not strong and will generally always require a length adjustment. Such adjustments are difficult and extremely time consuming in the case of a large truss structure. Furthermore, this arrangement does not lend itself to easy reconfigurability.
Yet another known technique utilizes pipe unions. That is, an internally threaded member grips a portion of a strut and threadably engages an externally threaded stub or protrusion on a node. In this manner, the strut is brought into engagement with and secured to the node. As was the case with the first previously described known technique, joints created in this manner are heavy in addition to being costly.
In view of the foregoing, it should be appreciated that it would desirable to provide a reconfigurable, high precision, highly stable truss structure. It should also be appreciated that is would be desirable to provide an improved method and apparatus for joining struts to coupling nodes to form reconfigurable, high precision truss structures. Finally, it would desirable to provide an apparatus for joining a strut to a coupling node that is lightweight, relatively inexpensive, simple in its construction and deployment, and capable of substantially reducing the above-described problems associated with hysteresis and stiction. Additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and following detailed description of a preferred exemplary embodiment and appended claims.
In accordance with a first aspect of the invention, there is provided a strut assembly that comprises a longitudinal member having a wall and at least a first substantially hollow end portion. A first threaded member is slidably mounted within the first end-portion and is capable of movement along a longitudinal axis of the member between a retracted position and an extended position. The wall has a first access opening therein for providing access to the first threaded member.
According to a further aspect of the invention there is additionally provided at least a first node having at least one internally threaded radial bore therein configured to threadably engage the first threaded member when the first threaded member is in an extended position.
According to a still further aspect of the invention there is provided a truss structure comprising a plurality of struts and a plurality of nodes. Each strut comprises a longitudinal member having at least a first substantially hollow end portion and having a wall. A first threaded member is slidably mounted within the first end portion and is capable of movement along a longitudinal axis of the member between a retracted position and an extended position. The wall has a first access opening therein for providing access to the first threaded member. Each strut includes a second substantially hollow end portion and a second threaded member slidably mounted within the second end portion and capable of movement along a longitudinal axis of the member between a retracted position and an extended position. The wall has a second access opening therein for providing access to the second threaded member. Each of the plurality of nodes includes at least a first internally threaded bore therein configured to threadably engage one of the first or second threaded members in one of the plurality of struts in its respective extended position.